fix: LongList read from file

[thenswan]

Description:
This PR introduces various fixes and improvements to the Long List family and its tests:

• LongListHeap fixes:

  • Resolved an issue where snapshots failed if the valid range did not start at index 0.

• AbstractLongList fixes:

  • Addressed a problem where writing and then reading an empty snapshot failed.
  • Addressed an issue where loading an empty Long List with a previously set valid range (e.g., 0 to a specific value) caused incorrect initialization of minValidIndex, maxValidIndex, and size.

• Refactoring AbstractLongList (and its subclasses):

  • Moved chunk orchestration logic into readBodyFromFileChannelOnInit() and delegated chunk-specific reading to a new readChunkData() method in subclasses.
  • Extracted repetitive code.

• Improvements to AbstractLongListTest (and its children):

  • Added tests to cover more edge cases.
  • Fixed existing tests (e.g., AbstractLongListTest#writeReadEmptyList() had a bug).
  • Consolidated LongList tests into AbstractLongListTest (migrated them from child classes).
  • Ensured snapshots from one implementation (e.g., LongListHeap) can be loaded by another (e.g., LongListOffHeap).
  • Renamed LongListTest to LongListAdHocTest; moved some tests into AbstractLongListTest.
  • Improved code structure (renamed methods/variables, added inline comments, etc.).

Notes for reviewers:

• Skipped using LongListDisk#resetTransferBuffer() in the refactored AbstractLongListTest as it seems unnecessary.
• Possibly convert ordered tests in AbstractLongListTest to regular tests.
• Please resolve any outdated comments. 🙏

Related issue(s):
Fixes #16652

Checklist

• Documented (Code comments, README, etc.)
• Tested (unit, integration, etc.)

[codecov]

Codecov Report

Attention: Patch coverage is 92.53731% with 5 lines in your changes missing coverage. Please review.

Project coverage is 68.95%. Comparing base (829e18c) to head (49de0c1).
Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
...swirlds/merkledb/collections/AbstractLongList.java	91.17%	1 Missing and 2 partials ⚠️
...com/swirlds/merkledb/collections/LongListDisk.java	88.23%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #16994      +/-   ##
============================================
- Coverage     68.96%   68.95%   -0.01%     
- Complexity    22763    22770       +7     
============================================
  Files          2619     2619              
  Lines         98283    98288       +5     
  Branches      10185    10185              
============================================
+ Hits          67777    67779       +2     
- Misses        26675    26677       +2     
- Partials       3831     3832       +1     

Files with missing lines	Coverage Δ
...com/swirlds/merkledb/collections/LongListHeap.java	89.13% <100.00%> (-8.75%)	⬇️
.../swirlds/merkledb/collections/LongListOffHeap.java	91.80% <100.00%> (-1.35%)	⬇️
...com/swirlds/merkledb/collections/LongListDisk.java	84.14% <88.23%> (-1.17%)	⬇️
...swirlds/merkledb/collections/AbstractLongList.java	88.51% <91.17%> (+0.27%)	⬆️

... and 8 files with indirect coverage changes

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.00% (target: -1.00%)	✅ 97.01%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (829e18c)	98066	71457	72.87%
Head commit (49de0c1)	98071 (+5)	71460 (+3)	72.87% (+0.00%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#16994)	67	65	97.01%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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